A turbomachine comprises a gas turbine having a plurality of fixed vane stages and a plurality of moving blade stages carried by a rotor mounted on a turbine shaft. The turbine shaft is centered and guided in rotation by bearings that need to be fed continuously with oil in order to limit friction wear thereof.
A known device for lubricating a turbomachine bearing comprises:
an annular bearing support part mounted on the stator of the turbomachine and defining a lubrication chamber around the bearing; and
an annular cover having an inlet for oil for lubricating the bearing, the annular cover being mounted in sealed manner on a radial end face of the annular support part, sealing being provided by an annular gasket mounted between the support part and the cover, and said cover including an annular enclosure for a flow of pressurizing and cooling air, which enclosure is fed at its upstream end by ducts formed in the support part and opening out at their downstream ends in the radial end face of the support part around the annular gasket.
In operation of the turbomachine, the temperature of the pressurizing and cooling air flowing in the ducts of the support part and in the annular enclosure of the cover is about 200° C. This air serves essentially to pressurize the rear enclosure and also to cool the material situated close to said duct or to the annular enclosure of the cover, while portions that are further away from the support part and the cover, in particular the portions of the radial end face of the support part situated between the downstream ends of the above-mentioned ducts can reach temperatures as high as about 370° C.
The annular gasket situated close to the radial end face of the support part is thus locally exposed to high temperatures. This gasket is generally an elastomer gasket of the Viton® type with limited ability to withstand temperatures above 200° C. It is therefore not effective in sealing the lubrication chamber of the bearing, and, while the turbomachine is in operation, oil leaks can appear between the radial end face of the support part and the upstream end of the annular enclosure of the cover. These oil leaks increase the oil consumption of the lubrication device, and can also lead to coke being deposited on the components of the turbomachine situated close to the leak, which deposit can form hot points and reduce lifetime.